The present invention relates to a method and system for non-contact inspection of large concrete structures such as dams and canals.
The non-destructive evaluation systems currently used for the inspection of large concrete structures such as dams have several shortcomings. These systems typically comprised acoustic systems made up of an acoustic source for generating an acoustic wave or waves which travel through the dam or other structure and a plurality of sensors or detectors placed at various locations on the dam for sensing the acoustic waves. Perhaps the most important of the shortcomings of each systems concerns coupling the sensors to the dam. Typically, a large number of sensors are used and these sensors all must be placed in physical contact with the dam structure. In addition, the acoustic sources currently used rely upon local characterization to detect structural anomalies in the dam structure.
The invention is concerned with a non-contact method and apparatus for inspecting large concrete structures, such as dams, which provides an improved testing apparatus and affords better structural characterization. The invention enables accurate determination of the physical properties of an entire large concrete dam or similar large structure, including the properties of bulk and local modulus and compressive strength, and the area of a lift line or joint that is cracked or delaminated.
In accordance with one aspect of the invention, a method is provided for measuring the mechanical properties of a large concrete structure such as a dam or the like, the method comprising: transmitting an acoustic signal into the large concrete structure so as to produce acoustic waves in the structure; transmitting a laser beam onto a surface of the structure such that the laser beam is modulated by the acoustic waves in the structure and is reflected from the surface of the structure; receiving the modulated reflected laser beam; and processing the received laser beam to derive data relating to at least one mechanical property of the structure.
Preferably, the time of travel and the degree of attenuation of the acoustic waves are determined and used in calculating a mechanical property or properties of the structure.
In accordance with a further aspect of the invention, a non-contact inspection apparatus is provided for determining mechanical properties of a large concrete structure such as a dam or the like, the apparatus comprising: a steerable acoustic source for transmitting an acoustic wave into the concrete structure; a laser source for transmitting a laser beam onto a surface of the concrete structure so as to interact with the acoustic wave such that the laser beam is modified by the acoustic wave and reflected from the surface of the concrete structure; a laser receiver for receiving the modified laser; and signal processing means for processing the modified laser beam received by said laser receiver to provide information about mechanical properties of the concrete structure.
Preferably, the steerable acoustic source comprises a stationary phased array. Advantageous, the phased array is a steerable electronically controlled phased array.
In accordance with a further aspect of the invention, a non-contact apparatus is provided for measuring mechanical properties of a large concrete structure, the apparatus comprising: a phased array for transmitting acoustic waves into the large concrete structure so as to produce acoustic waves in the concrete structure; a laser generator for transmitting a laser beam onto a surface on the concrete structure so as to sense the acoustic waves in the concrete structure, said laser beam being modulated by said acoustic waves and being reflected from the surface of the concrete structure; an interferometer for receiving the laser beam after reflection thereof from the surface of the concrete structure and for producing a corresponding output; and a signal processor for converting the output of said laser receiver into a signal relating to a mechanical property or properties of the concrete structure.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.